In these hard financial times I can understand about not wanting to spend any extra money. However, you have two choices that I can see. One you can do nothing and hope that it is nothing. By doing this if it is a start of a cavity and you do nothing then you are running risk of the issue becoming a much larger issue. (root canal, extraction ) which will lead to a high expense to fix.
Or you can go to the dentist now to make sure exactly what it is that you may or may not have. That you stated you do not have dental insurance you may wish to think about getting a dental discount plan. They have a very low monthly cost and it will help reduce you cost at the dentist for services render. I listed a link for that.
I hope this has helped